This invention concerns a method for the lateral compacting of slabs and the relative device.
The device according to the invention is located in a rolling line at least upstream of the finishing rolling mill stands so as to apply an action of compression on the lateral edges of the slab passing through in order to produce a reduction of width thereof and, at the same time, a compaction of the crystalline structure of the slab.
The usual layouts of rolling lines provide for the slab passing through to undergo a succession of passes in rolling mill stands having the axes of their rolls alternately horizontal and vertical so as to achieve progressive reductions of the thickness-width of the slab.
The rolling mill stands having the axis of their rolls vertical are commonly called "vertical edgers".
This alternation of horizontal-vertical passes also causes an effect of progressive compaction of the crystalline structure of the steel with a resulting reduction of the interstitial hollows and therefore an improvement of the superficial and inner quality of the finished product.
However, the compression action achieved by means of the vertical rolls, which carry out this compression by rolling, has been found more and more inadequate for achieving the quality standards which the market now requires.
Moreover, this rolling action has been found ineffective for great reductions of width inasmuch as this process produces only a localised swelling at the edges but has a very limited effect on the material in the body of the slab.
Embodiments have therefore been developed which can be introduced into a rolling line having a substantially continuous cycle and which have the purpose of improving the effectiveness of this lateral compression action and thus the quality levels that can be achieved without thereby affecting the production capacity of the line.
The state of the art has included embodiments which employ pressure systems associated with the lateral edges of the slab passing through.
One of the main purposes of these pressure systems is to achieve considerable reductions of width of the slab, up to 350 mm., in such a way as to increase the range of strip which can be produced, starting from the same one width of the slab.
This result, as we said above, cannot be achieved with the vertical edgers, which swell only the zone next to the edges which then becomes enlarged again in the horizontal rolling mill stands, and therefore the net residual reduction which can be achieved with those edgers is about equal to 20% of that which can be achieved with the press systems.
The economic justification of the press systems is substantially based on the increase of output of the continuous casting machine, which works without any change of format, on the reduction of the range of the variety of the slabs and on the improvement of the yield owing to the reduction of the discards of the leading and trailing end portions.
Press systems have been disclosed both of an alternate start-stop type with feed of the slab in steps and pressure on the slab when halted, and also of a continuous "flying" type, whereby the slab continues to move forward even during the pressure step.
The embodiments of the state of the art, however, have been found unsatisfactory in terms of complexity of the structure, complexity of the working cycle, difficulty of gauging to obtain the desired result in terms of reduction of width, poor versatility and worse adaptation to the variations of the conditions of the rolling cycle and owing to still other problems.
Moreover, the embodiments of the state of the art entail a great vertical bulk, which creates also great problems when it is necessary to perform maintenance and/or replacement of parts.
Furthermore, in the embodiments of the state of the art the adjustment of the reduction of width of the slab is achieved either by displacing transversely the whole structure which contains the crankshafts or by interposing auxiliary adjustment elements between the connecting rod coupled to the crankshaft and the die-holder body.
It is obvious that this adjustment entails halting the line, long times and great difficulties of corrective work, the use of labour, additional costs, poor versatility, poor accuracy of adaptation and still other problems.
JP-A-6-304611 discloses a press with crankshafts with the axis on the same plane but at a right angle to the plane of positioning of the slab to be worked.
This document teaches to include a single connecting rod element conformed as a cylinder-piston.